I have removed the float bowls, main jets and holders, and pilot jets. I cannot determine what the tube structure circled in the photo is and whether I need to clean or remove it. It does not appear to be removeable. Thank you in advance for any input.

Take a piece of wire from a wire brush and run it into the hole a few times to help clean out the dirt. Then do the air and carb cleaner. Also, do the wire on the main and the slow jets to see if they are "real" clean.